Scavenging/Capnography/CO2 - EXAM 2 Flashcards
recommended max level of volatile anesthetic alone
2 ppm
Definition of Scavenging
COLLECTION of excess gases from equipment used in administering the anesthesia exhaled by the patient
REMOVAL of these excess gases to an appropriate place of discharge outside of the working environment
recommended level of NO
25 ppm
recommended level of VA + NO
0.5 ppm
5 basic components of a scavenging system
gas collecting assembly transfer means scavenging interface gas disposal tubing gas disposal assembly
what are the widths of the transfer means tubing?
19 mm or 30 mm
Within the gas collecting assembly, what happens when the patient expires and it goes into the reservoir bag…?
the APL will pop off to allow excess pressure or volume out into the scavenge
Within the gas collecting assembly, what happens if the patient exhales through the vent?
the ventilator relief valve will pop off for the gas to move into the scavenging system
at what point is a little bit of volume removed from the circuit?
at the gas analyzers or capnography part
what happens to the volume of gas removed from the circuit?
it also goes into the scavenging system
what does the gas collecting assembly do?
captures gas at the site of emission
delivers gasses to the transfer means
what does the transfer means do?
conveys gas from the collecting assembly to the interface
Describe the structure of tubing in the transfer means
short and wide to accommodate large volumes without a significant increase in pressure
has female-fitting connectors on both ends
must be kink resistant with stiffer tubing
colored yellow
what is the function of the scavenging interface?
prevents pressure increases or decreases in the scavenging system from being transmitted into the breathing system
How could negative or positive pressure be created in the scavenging system?
positive - created by PPV
negative - created by the vacuum
what is the range of pressure that the interface will allow?
0.5 - 5 cmH2O
describe the structure of the interface tubing
30 mm male connecter
should be situated very close to the gas collecting assembly
what are the 3 basic elements of the interface?
positive pressure relief - protects patient in the event of an occlusion
negative pressure relief - limits subatmospheric pressure
reservoir capacity - matches the gas flow of the collecting assembly to the continuous flow of the disposal system
what are the 2 types of interfaces?
open or closed
open type interface
hard rigid casing with holes at the top
any excess volume that comes in will blow out the holes
the holes can be connected to a vacuum system to evacuate the gas
what are the benefits of the open interface system?
only uses a vacuum and the environment
there are no valves to control
you can’t generate any excess positive or negative pressure
what sort of adjustments can you make in the closed type interface?
there are separate valves for positive and negative relief and you can dial them up or down for how much pressure you want to let out of the system
In the open type interface, what factor is important to consider when you’re deciding on the suction level of the vacuum?
the rate should be higher than the rate of FGF so as to not create OR pollution
how does the positive pressure relief valve work on the closed type interface?
passive disposal – no vacuum used and no reservoir bag needed
it will open when a max pressure is reached
How does the negative pressure relief valve work in conjunction with the PPRV in the closed type interface?
- uses a reservoir bag
- has an active disposal system with a vacuum control valve to prevent reservoir bag from overinflation or complete collapse
what is the “backup” for the NPRV and PPRV used in a closed system?
a back up negative pressure relief valve will open at -1.8cmH2O if the primary mechanisms have failed for some reason
describe the structure of the gas disposal tubing
should be a different COLOR AND SIZE than the breathing system
should be short and wide
usually run overhead to prevent kinking or obstruction
Where is the gas disposal tubing located?
between the interface and the disposal assembly
what are the 2 types of a gas disposal assembly?
active - gasses move because of mechanical flow which creates negative pressure in the tubing and requires a NPRV
passive - pressure in the system exceeds atmospheric pressure when the patient exhales or the reservoir bag is squeezed (requires positive pressure)
What are the advantages and disadvantages of a passive type disposal system?
Advantages - simple to set up, inexpensive
Disadvantages - may be impractical in some buildings
How are waste gases removed in a passive system?
through an open window or a fan to the outside air
what are the advantages and disadvantages of an active type disposal system?
advantages - convenient in large hospitals with multiple machines running
disadvantages - major expense to set up this system, needle valves need continuous adjustment
How is gas removed in an active type disposal system?
the exhaust is connected to a hospital vacuum system via an interface that is controlled by a needle valve
how do you do a scavenging system check?
- ensure proper connection b/w the scavenging system, APL valve, ventilator relief valve
- occlude the Y piece and completely open the APL valve
- with minimal O2 flow, allow the reservoir bag to collapse completely and make sure that the pressure gauge reads 0
- turn on the O2 flush and allow the scavenger bag to fully distend but verify that the pressure gauge read less than 10 cmH20
- then turn off the O2 flush and make sure that the gauge doesn’t read less than 0
what is the danger in forgetting to check the scavenging system before a case?
there is no alarm system if the system fails during a case
Why do we use capnography?
confirm ETT placement
to determine if patient has effective ventilation
to detect abnormalities in V/Q ratio
What are some of the abnormalities that could potentially be discovered through the use of capnography?
PE - ETCO2 will be low MH disconnect in the system obstructed airway hypotension - really low ETCO2 b/c you aren't perfusing
under what circumstances would ETCO2 increase?
hypoventilation (low RR or low Vt)
obstructive respiratory disease (patient takes longer to exhale CO2)
increased metabolism (MH, stress, sepsis)
decrease in FGF (CO2 scrubber kicked, rebreathing)
When would ETCO2 decrease?
hypothermia hyperventilation low CO hypovolemia leak in the system (false low CO2)
How can you determine PaCO2 from ETCO2?
Under GA, PaCO2 is generally 2-5 mmHg less than ETCO2
what are the 2 methods for assessing the CO2 content of expired gas?
colorimetric or infrared absorption spectrophotometry
how does colorimetric CO2 measurement work?
CO2 combines with H2O on the paper and forms carbonic acid that turns the paper a different color
How does infrared absorption spectrophotometry work?
when the gas is exhaled the proportion of its components is analyzed and each gas will absorb infrared radiation at different wavelengths
mainstream capnography
a airway adapter hooked up to a transducer is placed directly on the end of the breathing circuit where the patient exhales
what are the disadvantages of using mainstream capnography?
potential for burns b/c it generates lots of heat
it can be heavy, causing kinks in the ETT
mucous can block the system from reading correctly
What are the advantages of using mainstream capnography?
there is less of a time delay
how does the sidestream capnography work?
takes a fixed volume from the circuit away from the patient and uses IR analysis to compare the CO2 sample with a known quantity
What are the advantages of using sidestream capnography?
gas it taken away from the patient and less potential for burns
what are the disadvantages of using sidestream capnography?
there is a slight time delay
potential disconnect source
dilution of the sample in pediatric patients r/t lower Vt
water vapor can condense in the system and filters are required
What is Phase 1 of the capnography waveform?
inspiratory baseline
no CO2
dead space gas is exhaled
What is Phase 2 of the capnography waveform?
the expiratory upstroke that represents rising CO2
mixture of alveolar and dead space gas
slope of the upstroke determined by evenness of alveolar emptying
At what point does the machine measure the ETCO2?
at the end of Phase 3
What is Phase 3 of the capnography waveform?
the longest phase (called the alveolar plateau)
end expiration
a reflection of PACO2 and PaCO2
What is phase 4 of the capnography waveform?
beginning of inspiration
CO2 levels rapidly decline to a normal inspired value
What are the 5 characteristics of the capnography waveform that are important to consider?
frequency rhythm height baseline shape
presence of stable CO2 for ***** breaths indicates tracheal intubation
3
What type of changes will be noticed on the capnography waveform for a patient with obstructive disease
slow rate of rise in Phase 2
little or no Phase 3
What sort of waveform will you have if the ETT has gone into the esophagus?
no consistent waveform, progressively decreasing waves
How will you know if rebreathing occurs?
if your inspiratory baseline continues to remain above 0 at the end of phase 4
what are some causes of rebreathing?
decrease in FGF, exhausted CO2 scrubber, dead space caused by equipment
how can you tell that your patient has started to spontaneously ventilate by using the capnography waveform?
there will be a curare cleft, or a small deflection, in the phase 3 portion of the waveform
means that the patient is starting to wake up from their neuromuscular blockade and the diaphragm is moving
what is the problem with noting cardiac oscillations?
NOTHING - they’re normal
what are some of the causes of rising CO2 is ventilation-related factors have been excluded?
Malignant hyperthermia
tourniquet release (releases lactic acid and metabolic byproducts)
release of aortic clamp
IV bicarb administration
CO2 blowing into peritoneal cavity
equipment failure (CO2 exhausted, expiratory valve stuck)
What are some causes of a decreasing CO2 tracing?
hyper ventilation
cardiac arrest
disconnect within the system
V/Q mismatch (r/t PE??)
What compound is the CO2 scrubber actually sensing?
H2CO3 - carbonic acid
what is the pattern of absorption in the CO2 scrubber?
from top to bottom
What are some of the more common types of absorbent?
Amsorb Plus
Soda Lime
Litholyme
Litholyme
made of lithium hydroxide
Soda lime composition
80% CaOH2
15% H2O
4% NaOH
trace silica and KOH
Why is water added to the CO2 scrubber system?
to facilitate the reaction to CO2 to form the carbonic acid
why is silica added to soda lime?
to increase hardness and prevent dust from forming
What is the average absorptive capacity of a soda lime scrubber?
26L/100g
On average, how much CO2 is released by a non-stressed person each hour?
12L CO2
What are the chemical reactions as CO2 moves through a soda lime scrubber?
CO2 + H2O = H2CO3
H2CO3 + 2NaOH = Na2CO3 + 2H2O + heat
Na2CO3 + CaOH2 = CaCO3 + 2NaOH
*can also use KOH;K2CO3
Composition of Amsorb
80% calcium hydroxide
16% H2O
1-4% calcium chloride
trace calcium sulfate for hardness
absorptive capacity of amsorb
10L/100g
What chemical reactions take place when CO2 enters an amsorb scrubber?
CO2 + H2O = H2CO3
H2CO3 + CaOH2 = CaCO3 + 2H2O + heat
When should you replace your CO2 absorber?
when its at 50-70% color change
what is the ideal shape of the absorbent crystals? why?
4-8 mesh
to create ideal surface area without increasing resistance
what should the hardness number be for the granules?
> 75
what is “channeling”?
preferential passage of gas through the absorber via pathways of least resistance
results from loosely packed crystals
How can you prevent channeling?
shaking the canister around a little bit before you use it
dry soda lime may degrade inhaled anesthetics to ****
Carbon monoxide
What is the danger with leaving an oxygen source on over night, running through the scrubber?
carbon monoxide will build up in the system and could cause poisoning
How can you prevent degradation of the VA/scrubber?
run your flows at a rate of at least 2L/min
what can sevoflurane/halothane degrade to when it passes through soda lime?
Compound A = nephrotoxic
What are some safety considerations when using a CO2 scrubber?
change it every morning
turn off gas flows when not in use
change all absorbent, not just one canister
keep flows low to preserve humidity
